Multi-station printing system

ABSTRACT

A multi-station printing system with a screen printer at each of the stations for printing on an intermittently travelling continuous web of material which is stopped in accurate registry at each of the stations, an air dryer between stations for drying the web and by means of negative pressure created by air flow imparting a drag on the web for proper handling thereof in guiding and registry, and control means for accurately positioning the web for printing at each station and for permitting operation of one station independently of the others.

United States Patent [191 Seedorf [451 Nov. 19, 1974 [52] U.S. Cl 101/115, 101/126, 101/196,

101/288, 226/30, 226/33 [51] Int. Cl. B4lf 15/10, B411 15/24 [58] Field of Search 101/115, 181, 126, 124,

[56] References Cited UNITED STATES PATENTS 1,873,057 8/1932 Smith 226/33 2,034,694 3/1936 Dansmann. 101/181 3,013,459 12/1961 Co1eman.... 226/33 3,013,487 12/1961 Faeber 3,316,836 5/1967 Epstein 101/117 3,323,700 6/1967 Epstein et a1.. 226/39 3,499,233 3/1970 Black 101/115 3,525,872 8/1970 Schneider 101/196 3,550,828 12/1970 Watson 226/30 3,623,808 11/1971 Baasner et a1. 226/33 3,664,561 5/1972 Feiertag 226/21 3,724,732 4/1973 Bonner 226/21 3,729,079 4/1973 Zenner et a1 197/1 R 3,777,960 12/1973 Weinert et al. 226/39 3,780,651 12/1973 Black et a1 10 1/115 FOREIGN PATENTS OR APPLICATIONS 480,223 1/1952 Canada 271/22 Primary Examiner-Robert E. Bagwill Assistant Examiner-Wi1liam Pieprz Attorney, Agent, or Firm-Wegner, Stellman, McCord, Wiles & Wood [5 7] ABSTRACT A multi-station printing system with a screen printer at each of the stations for printing on an intermittently travelling continuous web of material which is stopped in accurate registry at each of the stations, an air dryer between stations for drying the web and by means of negative pressure created by air flow imparting a drag on the web for proper handling thereof in guiding and registry, and control means for accurately positioning the web for printing at each station and for permitting operation of one station independently of the others.

2 Claims, 7 Drawing Figures HOVISISM PATtNTtu 3 0F 8 3.848 528 PATENTEL HOV 1 91914 SHEET 5 BF 6 ZOJE MULTI-STATION PRINTING SYSTEM BACKGROUND OF THE INVENTION This invention pertains to a multi-station printing system with a screen printer at each station with means for accurately registering an intermittently travelling continuous web at each station prior to printing and with dryer means between the stations for drying the web and imparting a drag thereto to provide for accurate guiding and web registry.

The prior art known to the applicant for multistation screen printing has used a continuous belt or other support for a web or sheet material to carry the material through successive stations. Another type relies upon wheels at printing stations with pins to engage perforations in the web. Such devices have resulted in expensive, complex and inaccurate mechanisms which must be designed and built for a particular application.

SUMMARY OF THE INVENTION bers of stations to handle a web of material with control of the web feeding and guiding, enabling independent operation of the screen printer at each station. Additionally, the system includes a dryer between each of the stations for drying the web preparatory to the next printing operation thereon, with the dryer constructed to utilize the drying air flow to provide a negative pressure to apply tension or a drag to the web to facilitate its handling both in edge guiding thereof and obtaining registry at a printing station.

An object of the invention is to provide a multistation printing system with a screen printer at each of the stations for printing on a section of continuous web including means for accurately locating the travelling web in stopped position at each of said stations and with means for operating each of said stations independently of the other whereby any desired number of stations may be provided by joining together a plurality of station units and their controls.

Another object of the invention is to provide a multistation printing system as defined in the preceding paragraph wherein accurate registry of the web at each of the stations is provided by web feeding means including a driven vacuum roller and web brake means with a control system for scanning a registry mark to reduce the speed of web travel by reducing the speed of the driven roller and for subsequently scanning a registry mark to obtain instantaneous stopping of the web and with the driven roller having a yieldable relation with the web whereby the driven roller does not interfere with the stopping of the web by the web brake means.

mark scanned is a mark that was printed at the same time as the printed matter within the printing area at the succeeding station.

A further object of the invention is to provide a mu]- ti-station printing system as defined in the preceding paragraphs wherein a dryer for the web is positioned between each of the stations and with the dryer constructed to utilize the drying air flow to'create a negative pressure in a manner which exerts a drag on the web to facilitate accurate controlled handling thereof and more particularly wherein the dryer has a pervious plastic surface through which the drying air may flow to an air exhaust at the side of the pervious surface opposite that which engages the web whereby a negative pressure draws the web against the pervious surface and with the surface being sufficiently slippery to permit continued movement of the web as caused by the driving roller at a printing station. The pervious plastic surface may be stationary or be a belt moving with the web withsuitable retarding of the belt.

An additional object of the invention is to provide a multi-station printing system wherein the drive roller at the stations beyond the first station is responsive to scanning means at the particular station for reducing its speed preparatory to stopping of the web and is also responsive to the size of a web loop in advance of the dryer associated with that station whereby reduction in the size of the loop to a predetermined level will also reduce the speed of the driving roller at the successive station to permit build-up of the loop.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a vertical, central, longitudinal section of a part of the multi-station printing system;

FIG. 1B is a view, similar to FIG. 1A, showing the remainder of a multi-station printing system;

FIG. 2A is a plan section, taken generally along the line 2A2A in FIG. 1A;

FIG. 2B is a plan section, taken generally along the line 2B--2B in FIG. 18;

FIG. 3A is a schematic of the electrical and pneumatic circuit showing the circuit common to each station;

FIG. 3B is a schematic of part of the circuit used for each succeeding station after the first station; and

FIG. 3C is a schematic of the circuit for controlling rewind of the web.

DESCRIPTION OF THE PREFERRED EMBODIMENT The general views of the drawings show the multistation printing system as comprising an unwind stand in dicated generally at 10 for a roll of web material 11 with the web travelling to a first printing station, indicated generally at 12, and then to a second printing station, indicated generally at 15, and then to a rewind The unwind stand has a movable frame mounted for lateral movement on rails 21 and 22 and carries a mandrel 23 mounting the roll 11. The lateral position of the frame and web roll 11 is controlled by a conventional edge guide system including a sensing head (not shown) which detects the lateral position of the web and when correction is required operates a cylinder 25 for lateral positioning of the frame 20. Also, as is known, the mandrel 23 has an electric brake 24 associated therewith which is responsive to the position of an adjustable weight dancer idler roll 26 in a loop 27 of the web. The position of the dancer idler roll controls a potentiometer 28 which controls the application of the mandrel brake. The mandrel 23 is non-driven, with the web being drawn from the roll and the brake imparting a drag to mandrel rotation when required as detected by the dancer idler roll.

The mechanism in each of the printing stations and the dryer structure therebetween is shown supported on a framework having a pair of longitudinal spaced apart beams 30 and 31 which are spanned by transverse braces 32 and 33 suitably secured to the beams 30 and 31 and also to vertically extending floor engaging supports 34 and 35.

The screen printing mechanism at the first printing station 12 includes a base mounted on suitable transverse support members 41 and 42 supported on the longitudinal beams 30 and 31 and having a bed 43 provided with vacuum means, as generally known, to hold the web W in position for printing when the vacuum is applied. A screen frame 44 is mounted above the bed 43. A squeegee moves both vertically and iongitudinally of the screen to print upon the web W. This squeegee is shown at 45 in FIG. 3. The general structure of the screen printing mechanism is conventional and includes pneumatically operated cylinders for obtaining desired movements including a squeegee cylinder 46 which lowers the squeegee to print position relative to the screen and a print cylinder 47 which moves the squeegee 45 longitudinally of the screen for obtaining the transfer of the printing material through the screen to the web W.

The web feeding means and means for providing web registry at the station 12 include a drive roller 50 having a perforate cylindrical surface 51 with a vacuum applied through the interior thereof to the approximate upper half of the roller through a vacuum connection 52 whereby the drive roller 50 yieldably holds the web W to impart movement thereto in response to rotation of the drive roller. The drive roller 50 is driven by an infinitely variable, potentiometer-controlled motor 55 through an electric clutch 56 connected to a belt drive 56a which drives a shaft 57 of the roller. The shaft 57 is mounted in bearings 58 and 59, mounted on the longitudinal beams 30 and 31, respectively. The drive roller 50 imparts movement to the web but is not used to control accurate location ofthe web at the printing station.

An idling brake roller 64 is mounted on a shaft 65 carried by bearings 66 and 67 on frame members extending vertically upward from longitudinal beams 30 and 31. One of the frame members extending upwardly from the beam 30 is shown at 68. This idler roll 64 has the web W passing thereover in the travel of the web to the screen printer and normally idles. Preparatory to stopping the web at the station, a pressure roller 70 is brought into engagement with the web to press it against the brake roller 64 and subsequently an electric brake 71 connected to the shaft 65 is operated to stop brake roller and stop web W. The pressure roller 70 is carried at its ends by a pair of arms 75 and 76 fastened to a rotatably mounted shaft 77 which is connected by an arm 78 to the rod 79 of an air cylinder 80.

A pair of photocells and 86 are suitably mounted from the frame and are positioned to scan a registry mark on the web W and through a circuit, to be described, initially causing a slowdown in the rate of advance of the web followed by accurate stopping of the web in the proper position relative to the screen 44 of the screen printer. The motor 55 has two adjustably-set speeds selected from the infinitely variable speed curve of the motor. At the first station, a pair of registry marks, indicated at 88 and 89, are printed on the web at the leading and trailing edges of the impression area, respectively. The registry mark 88 then functions with the photocells 85 and 86 to cause slowdown and stopping of the web with minimal spacing between successive impression areas on the web and while the trailing registry mark 89 may still be within the perimeter of the screen printing structure and not in position to be scanned at the first station.

With the web stopped, the printing operation is then performed at the first station 12 followed by a resumption of feeding of the web and the web travels to a dryer 17 after passing through a loop formation indicated generally at 90.

The dryer l7 embodies a casing having a top panel 91 and side panels 92 and 93 along with end panels which form an enclosure having an open lower end spanning the space between the frame beams 30 and 31. A hollow cabinet is positioned within the casing and has a top wall 94 and perforate side walls 95 and 96 which, with enclosing end walls, form a negative pressure chamber. The casing has an inlet opening 97 for entry of heated air at a relatively high velocity which passes through a nozzle plate 97a and circulates through the cabinet, as shown by the arrows, and then through the perforate walls into the negative pressure chamber for exhaust through an air outlet 98.

The web W after leaving loop 90 travels upwardly in the dryer casing and then changes to a downwardly travelling direction by passage about rollers 99 and 100 and exits at the lower end of the dryer casing. The air flow through the dryer results in a negative pressure within the negative pressure chamber which draws the web against the surface of the negative pressure chamber to provide a drag or tension on the web. It has been found that this action is facilitated by the use of a covering over the negative pressure chamber which, as shown, is in the form of a pervious belt of mesh plastic, such as polypropylene, which is fixed over the negative pressure chamber and which is tied at its lower end 102. This belt of plastic material 101 is relatively slippery, whereby the negative pressure may hold the web against the negative pressure chamber surface but still permit travel of the web. The belt may be movably mounted for travel with the web, but with drag means to exert a drag on travel of the belt.

As the web W leaves the dryer 17, it passes downwardly to an edge guiding and web centering unit having an adjustable frame adjustable about a vertical axis with a pair of guiding rollers and 111 mounted on the frame 112. This web guiding structure is well known in the web feeding art and includes a mechanical or electronic sensing device positioned along an edge of the web to detect variance in the path of travel and correspondingly adjusts the frame 112 and the rollers 110 and 111 to bring the web back to proper tracking relation. The retardation of the web by the dryer 17 maintains proper tension on the web enabling the guiding unit to perform properly in guiding the web. In view of the conventional nature of such structure, it is shown only generally and reference may be made to the prior art for specific details thereof.

The web W travels upwardly to the second printing station and travels about a brake roller 115 having a coacting pressure roller 116 with an air cylinder 117 for positioning thereof similarly to the brake roller 64 and pressure roller 70 of print station 12. Generally, the structure at the print station is the same as at station 12 and need only generally be referred to. This structure includes the variable speed vacuum drive roller 120 operated by a motor 121 and the vacuum bed 125 associated with the screen frame 126 and with the parts operable in the same manner as the corresponding parts at print station 12. At this station, the photocells for controlling slowdown and stopping of the web are arranged differently from those at station 12. The photocell 130, as shown, is located beyond the printing element for scanning either of the marks 88 or 89 printed on the web and is in circuit to provide for slowdown of the vacuum drive, roller 120. The photocell 130 could be located in advance of the printing element. A second photocell 131 is located adjacent the printing elements and positioned to scan the trailing registry mark 89 which has been made at the same time as the impressions located within the printing station. Extreme accuracy is obtained because of the scanning of the registry mark made at the same time as the printed matter with which registry is to be maintained at the second print station 15. Also, there is uniformity of stopping at each station because the web is at a uniform slow speed at all stations when the mark is sensed. This use of the trailing registry mark is possible because the print area at the second station is smaller than at the first station.

As more fully described in connection with the circuit, the vacuum drive roller 120 is not only subject to the slowdown signal provided by photocell 130 but is also subject to slowdown dependent upon thesize of the loop 90. A photocell 140 detects when the loop 90 shortens beyond a permissible limit and when such occurs the speed of motor 121 is reduced to reduce the speed of vacuum drive roller 120 until the loop 90 exceeds the permissible minimum limit. At each print station, the web passes from the flat part of the bed of the screen printer onto a sloped leaving edge which is inclined downwardly toward the vacuum drive roller to reduce the minimum space on the web between successive printings. An intermediate support plate 141 supports the web. The web W after leaving the vacuum drive roller 120 passes through a loop 145 and then into the dryer 18 which is of the same construction as dryer l7 and from the dryer the web passes around a pair of rollers 150 and 151 of an edge guide and web centering mechanism similar to that following the dryer [7. The web then travels to a brake roller 152 having a pressure roller 153 operable by an air cylinder 154 with this construction being the same as for brake rollers 64 and 115. The web then travels to the rewind stand 16.

The brake roller 152 and pressure roller l53are controlled from a photocell 160 which detects a reduction in the size of the loop ahead of the dryer 18 beyond a minimum permissible limit. The circuit for photocell includes a time delay in signalling increase of the loop size.

The rewind unit 16 has a frame 161 which rotatably mounts a wind-up mandrel 162 supported by bearings 163 and 164 with the mandrel being driven by a belt 165 from a motor driven constant tension control unit 166.

The circuit is shown in FIGS. 3A, 3B and 3C with the part shown in FIG. 3A being typical for the control of the web feeding and printing mechanism at each printing station. The circuit is shown as a cross-the-line diagram between the power lines 200 and 201. The electronic eye 85 is connected into a relay box 202 which controls the solenoid 203 of an air valve for the pressure roller operating air cylinder 80. The relay also controls the relay coil 204R for deenergization thereof whereby the relay contacts 204R-1 and 204R-2 move to their normally closed position to place a potentiometer 205 into the control circuit for the motor 55 which drives the vacuum driving roller 50. This motor control circuit is indicated generally at 206 and is commercially sold under the name CADET CONTROL. With the actuation of the relay 202, the resulting shift in the circuit has caused reduction in the speed of the web W at the station 12 and shortly thereafter the photocell 86 scans the registry mark 88 to actuate the relay, indicated generally at 210R. This immediately actuates the brake 71 for the brake roller 64 by suitable means, such as a thyraton tube circuit, and also opens a normally closed switch 211 to deenergize a relay 212R. This permits relay contact 212R-1 to close and through line 215, having the normally closed contact 216R-2, the solenoid valves 217 and 218 are actuated to apply vacuum to the bed 43 of the print mechanism, and closes a vent valve therefor, respectively. This applies a vacuum to the bed 43 to hold the web W firmly in position preparatory to printing. The web will have stopped for applying the vacuum because of the rapid actuation of brake 71 compared to the relay actuation of the sole noid valves 217 and 218.

The presence of a vacuum in the vacuum bed 43 is sensed by a vacuum switch 220 which has contacts 221 and 222. The normally closed contact 222 is opened to deenergize the electric clutch 56 and drive train for the vacuum drive roller 50 whereby the vacuum roll is free to adjust and avoid placing of tension on the web W during the print cycle. Switch 221 is closed by the vacuum sensing switch 220 to act through a normally closed relay contact 216R-3 and energize a solenoid 225 for operating a three-way air valve 226 which is closed to supply air under pressure to the pneumatically operated components at the print station.

The main air supply from an air line 230 acts through lines 231 and 232 to lower the squeegee 45 of the print mechanism and operate the squeegee print cylinder 47. The air is supplied through a pilot operated reversing valve 235 with this valve being shiftable to apply air through a line 236 to the opposite ends of the cylinders 46 and 47 to reverse the operation of the squeegee. The position of the reversing valve 235 is dependent upon the position of the mechanically operated air valves 237 and 238 which are operable by the squeegee at the opposite ends of its stroke. Thus, as the squeegee 45 is moved to its right-hand limit position, the valve 238 is shifted to reverse the condition of the reversing valve 235 from the position shown. When the parts return to the position shown in the drawing, the valve 237 is actuated to return the reversing valve 235 to the position shown.

As the cylinder 47, operable during the print stroke, reaches the end of the printing stroke, the contacts on a switch 240 are closed, by a sliding actuator bar (not shown), which energizes relay 216R through a time delay relay indicated generally at 241. The use of the sliding actuator bar is known as in the printing machine offered by Rondec Screen Process Limited of London,

England. The delay in energization of relay 216R is provided so that relay contact 216R-3 will stay closed to maintain the three-way valve 226 in operative position to supply control air to the switching valves 237 and 238 which reverse the stroke of the cylinder 47. As is conventional of any screen printer, upon reversal of the cylinder 47, the squeegee lifts and a flood bar is lowered for the return stroke. Upon energization of relay 216R, the relay contacts 216R-2 and 2l6R-3 are opened as well as a relay contact 2l6R-1. The opening of the latter contact functions to reset the relay 210 operable by the photocell 86 which releases the electric brake 71 on the brake roller 64 and also energizes relay 212R. This latter operation opens the relay contact 212R-1 which deenergizes the solenoid valves 217 and 218 to close the vacuum valve and open the vent valve for the vacuum bed 43. This relief of the vacuum is sensed by the vacuum switch 220 to open contact 221 and close contact 222. With contact 221 open, as well as relay contact 216R-3, the three-way valve 226 is moved to open position by deenergization of the coil 225. The closing of contact 222 energizes the clutch 56 for the drive for the vacuum feed roller 50 to commence movement of the web W. During this interval, the air cylinder 47 has reached the end of its return stroke to engage the sliding actuator bar (not shown) to open the switch 240 which deenergizes the relay 216R to close relay contacts 216R-1, 216R-2 and 2l6R-3.

Additional control relay 250R has a relay contact 250R-l which is in the reset circuit of the relay 202. When the switch 240 was opened, this deenergized relay 250R whereby the relay contact 250R-1 closed to set the relay 202 for a repeat operation. The relay 250-R had previously been energized when the switch 240 was closed.

The cycle of operation has been completed and the circuit is conditioned for a repeat operation upon the next scanning of a registry mark 88 by the photocell 85 to commence the slowdown operation.

The foregoing circuit is typical of the general control circuit for the mechanism at each print station and is repeated in the circuit as many times as there are print stations.

There is an addition to the circuit for the print stations succeeding the initial station which relates to the modification of the web speed in second and succeeding stations, dependent upon the size of the loop preceding the respective station.

The additional circuit added for each station after the first print station is shown in FIG. 3B and provides a loop detecting circuit for additional control of speed of the web to provide slowdown when the loop shortens beyond a predetermined minimum limit. This additional circuit includes a relay, indicated generally at 300, which is across the lines 200 and 201 and has the photocell connected thereto for detecting the size of the loop 90. For clarity, the relay 300 is shown in association with parts of the basic control circuit for the web feed mechanism at a second and at succeeding stations corresponding to that described in FIG. 3A, including the relay 202 and the operating valve 203 for the pressure roller which in this instance is the pressure roller 116. Also, the relay 204R functions to reduce the speed of the motor 121 for driving the vacuum feed roller 120. As the loop 90 shortens, and light contacts the photocell 140, the relay 204R will be deenergized which, as previously described, puts the resistance 205 in the motor control circuit to reduce the speed of the vacuum drive roller. In all other respects, the web feed mechanism and print feed station 15 operates the same as that described for the mechanism at print station 12.

The control of the web loop preceding the rewind unit 16 is shown in FIG. 3C, with the photocell sensing shortening of the loop to actuate a relay 310 which causes energization of a four-way solenoid valve 311 for operating the pneumatic cylinder 154 which throws pressure roller 153 against the brake roller 152. Additionally, energization of the relay operates a brake 312 connected to the shaft of the brake roller 152 stopping travel of the web W to permit rebuilding of the loop 145 in advance of the dryer 18. The tension control unit 166 automatically holds tension on the web on the mandrel 162 until the web W is allowed to run free. Once the loop 145 has returned to the normal length, the relay 310 is deactivated with release of the brake 312 and deenergization of the solenoid valve 311, whereby the web can again be wound on the mandrel 162.

With the structure and circuit disclosed herein, it is possible to have a multi-station printing system with a desired number of printing stations required for multicolor operations merely by duplicating mechanism at each station and duplicating circuit control elements. The web upon which the impressions are made is directly controlled without the requirement of any supporting conveying mechanism and the printing mechanism at each station can operate independent of the others with necessary controls to maintain guiding and tensioning of the web for proper printing. The dryer construction for drying the web incidentally provides necessary back tension on the web. The printing area at the first print station is larger than at succeeding stations whereby a registry mark printed at the same time as the impression at the first station can be used for accurately stopping and locating the web at succeeding print stations while an additional registry mark printed at the first station may be used to advance the web at the first station only the required distance to advance a clear section of the web to printing location at the first print station which is particularly important when printing on relatively high cost web material.

I claim:

1. A multi-station screen printing system with a screen printer at each of the stations for printing on a section of continuous web while said web is stationary at a station; means associated with each of said stations for feeding and advancing the web into said station and stopping the web in response to a registry mark thereon and independently of web feeding means at other stations including, a drive roller beyond the screen printer, means for driving said drive roller at either a fast speed or a slow speed, intermittently operable means in advance of the screen printer for holding the web, and control means including means at the station for successively scanning a registry mark on the web for first reducing the drive roller from fast speed to slow speed and then upon a second scanning of said registry mark stopping the drive roller and activating the web holding means to hold the web in position for printing; and means for permitting independent operation of the screen printer at a station on a stationary web independently of the operation at another station including a web loop between said stations, and means for detecting the size of said loop and controlling the web feeding means at the next station beyond the web loop to maintain the loop to a predetermined dimension, said web holding means including a pair of rotatable rollers engaging the web therebetween and a relay operated brake for stopping rotation of said pair of rollers, and said drive roller is a vacuum roller which yieldably holds the web thereagainst whereby stopping of the web by said holding means is permitted by movement between the web and the vacuum roller.

2. A multi-station screen printing system with a screen printer at each of the stations for printing on a section of continuous web while said web is stationary at a station; means associated with each of said stations for feeding and advancing the web into said station and stopping the web in response to a registry mark thereon and independently of web feeding means at other stations including, a drive roller beyond the screen printer, means for driving said drive roller at either a fast speed or a slow speed, intermittently operable means in advance of the screen printer for holding the web, and control means including means at the station for successively scanning a registry mark on the web for first reducing the drive roller from fast speed to slow speed and then upon a second scanning of said registry mark stopping the drive roller and activating the web holding means to hold the web in position for printing; and means for permitting independent operation of the screen printer at a station on a stationary web independently of the operation at another station including a web loop between said stations, and means for detecting the size of said loop and controlling the web feeding means at the next station beyond the web loop to maintain the loop to a predetermined dimension, and wherein the screen printer at a first station prints leading and trailing registry marks and the screen printer at a succeeding station has a smaller printing area, said scanning means at said first station scanning the leading registry mark to stop the drive roll when the web is positioned for a succeeding printing operation at the first station with the trailing registry mark still in the screen printer area, and the scanning means at the succeeding station scanning the trailing registry mark impressed at the same time as the printed matter on the web which is at said succeeding station. 

1. A multi-station screen printing system with a screen printer at each of the stations for printing on a section of continuous web while said web is stationary at a station; means associated with each of said stations for feeding and advancing the web into said station and stopping the web in response to a registry mark thereon and independently of web feeding means at other stations including, a drive roller beyond the screen printer, means for driving said drive roller at either a fast speed or a slow speed, intermittently operable means in advance of the screen printer for holding the web, and control means including means at the station for successively scanning a registry mark on the web for first reducing the drive roller from fast speed to slow speed and then upon a second scanning of said registry mark stopping the drive roller and activating the web holding means to hold the web in position for printing; and means for permitting independent operation of the screen printer at a station on a stationary web independently of the operation at another station including a web loop between said stations, and means for detecting the size of said loop and controlling the web feeding means at the next station beyond the web loop to maintain the loop to a predetermined dimension, said web holding means including a pair of rotatable rollers engaging the web therebetween and a relay operated brake for stopping rotation of said pair of rollers, and said drive roller is a vacuum roller which yieldably holds the web thereagainst whereby stopping of the web by said holding means is permitted by movement between the web and the vacuum roller.
 2. A multi-station screen printing system with a screen printer at each of the stations for printing on a section of continuous web while said web is stationary at a station; means associated with each of said stations for feeding and advancing the web into said station and stopping the web in response to a registry mark thereon and independently of web feeding means at other stations including, a drive roller beyond the screen printer, means for driving said drive roller at either a fast speed or a slow speed, intermittently operable means in advance of the screen printer for holding the web, and control means including means at the station for successively scanning a registry mark on the web for first reducing the drive roller from fast speed to slow speed and then upon a second scanning of said registry mark stopping the drive roller and activating the web holding means to hold the web in position for printing; and means for permitting independent operation of the screen printer at a station on a stationary web independently of the operation at another station including a web loop between said stations, and means for detecting the size of said loop and controlling the web feeding means at the next station beyond the web loop to maintain the loop to a predetermined dimension, and wherein the screen printer at a first station prints leading and trailing registry marks and the screen printer at a succeeding station has a smaller printing area, said scanning means at said first station scanning the leading registry mark to stop the drive roll when the web is positioned for a succeeding printing operation at the first station with the trailing registry mark still in the screen printer area, and the scanning means at the succeeding station scanning the trailing registry mark impressed at the same time as the printed matter on the web which is at said succeeding station. 